docs: def ensure_default_namespace(self) -> Namespace:
          """Get or create the BEL default namespace."""
          namespace = self.get_namespace_by_keyword_version(BEL_DEFAULT_NAMESPACE, BEL_DEFAULT_NAMESPACE_VERSION)
  
          if namespace is None:
              namespace = Namespace(
                  name='BEL Default Namespace',
                  contact='charles.hoyt@scai.fraunhofer.de',
                  keyword=BEL_DEFAULT_NAMESPACE,
                  version=BEL_DEFAULT_NAMESPACE_VERSION,
                  url=BEL_DEFAULT_NAMESPACE_URL,
              )
  
              for name in set(chain(pmod_mappings, gmod_mappings, activity_mapping, compartment_mapping)):
                  entry = NamespaceEntry(name=name, namespace=namespace)
                  self.session.add(entry)
  
              self.session.add(namespace)
              self.session.commit()
  
          return namespace